Tonight's Season 5 finale of Pretty Little Liars answered the question, Who Is "A"? And the identity of "A" is...
Watch the reveal in the below video:
[Warning: Spoiler below]
Charles is "A"! Earlier in the episode, Spencer had a dream and the name "Charles" was spelled out to her in blocks. Later, Alison DiLaurentis, aka Mona, is announced as the prom queen. Then the girls unveil a crown to give to "Charles" as the prom king. He then appears, but is wearing a mask. The girls take a picture of him, causing a blackout, busting some of the fuses. They take off running. At the same time, the police discover the van at a farm that the girls used to go to when they were little. Toby leads them down into A's lair.
As the girls are running around, Spencer finds herself in a room alone and the power goes on. She then finds a slide projector of the farm and A comes up behind her. When Mona finds Spencer,”Charles” is gone. The girls make their way outside, but are fenced in with an electric fence. The music begins to play and the episode ends.